This invention relates to stereophonic sound systems and more particularly to equipment for analyzing the properties of sounds generated in multichannel sound systems.
When sound is recorded, transmitted or played using multichannel systems it is important to present the listener with as perfect a reproduction as possible of the original sound including the direction from which the sound may be perceived. A person listening to a sound source may sense variations in the relative loudness and phase of the sound received in his left and right ears. This loudness and phase information is combined in the mind of the listener to determine the "aural perspective" of the sound which may include not only the principal direction from which the sound appears to be emanating (its balance) but also the range of directions from which all parts of the sound appear to be coming (its separation) and the loudness of the individual parts of the sound over that range (its modulation). In order to maintain reproduction quality, sound engineers generally strive to maintain the loudness and phase of multichannel sound, which may be generally referred to as the "stereo image" of the sound, as close to original values as possible, although in select cases, they may attempt to manipulate the stereo image of the sound to produce certain special effects. In any event, reliable information about the stereo image and aural perspective of sound represented by multichannel sound signals (which regardless of the number of channels is generally referred to as "stereophonic sound") is necessary in order to make decisions about how to regulate the sound.
In the past, audio engineers have frequently used their own ears to determine the aural perspective of stereophonic sound. However, this requires a listening system of known calibration such as a specially designed audio room and is very difficult and time consuming work. Alternatively, audio engineers have used laboratory oscilloscopes electrically driven so that one channel of a stereophonic system is used to control the vertical deflection and another channel is used to control the horizontal deflection of the electron beam on the screen of the oscilloscope. These so-called "X.Y configuration" displays provide only limited amounts of information about the stereo images of the sounds by displaying arbitrary types of signals which suggest errors in the stereo image. X.Y configuration displays do not give the user any useful indication as to the details of the actual aural perspective of the sound.
The present invention provides a display which provides accurate and reliable information about the stereo image and aural perspective of stereophonic sound. The display includes signals which illustrate directly to the user the aural perspective of the sound including its modulation, separation and balance.
Further, the invention may be used to view and adjust the stereo image of the intended constituents of a composite sound on the individual channels of a multichannel recording system before each constituant is mixed into the composite to form the desired complex sound recording. Stereophonic sound may thereby be mixed without the need for a calibrated listening room.
Additionally, the present invention provides a display which quickly and positively indicates when stereophonic sound signals are completely out of phase and therefore incompatible for monoaural playback as may occur if one of the signals becomes electrically inverted.